Among the existing package structures for semiconductors, a package on package structure is one of the well-known package structures.
A typical package on package structure includes an upper package device, a lower package device, and an epoxy molding compound layer sandwiched between the upper package and the lower package device. The epoxy molding compound layer includes a number of receiving holes and a number of electrically conductive posts. Each electrically conductive post is received in a receiving hole for electrically connecting the upper package device and the lower package device. Each electrically conductive post is formed in the receiving hole by filling and solidifying electrically conductive paste.